Quick Double Nickel

iTrader: (5)

This is one I've been thinking about for a while, so I though I'd post it on here to see what everyone has to say.

While 100 horsepower per liter output from a large V8 motor, such as the LSx, is no new thing, retaining stock, or near-stock drivability, while doing so is. With the multitude of new combos coming on board with at or over 500 rwhp from a 5.7L it seems that we've hit that magical mark of 100 hp/L, but has the drivability suffered? These new combos seem to have cams in the 23x range at .050, which isn't much like stock in my opinion. I know a lot is to be gained in the tune of the engine with regards to drivability and ultimate power production, but there are a lot of trade-offs to get to that mark.

There have been a number of import car makers that have accomplished this in production cars with a multitude of different naturally-aspirated combinations (the 1999? 1.6L Si Civic, and 4.2L Audi V8 come to mind), but nothing from the domestic car makers and their proprietary V8s. So, the question is: How do you obtain this lofty goal and maintain production-spec drivability, emissions, and fuel consumption? Are DOHCs, VVT (and lift), or smaller motors the only way to accomplish this?

01CamaroZ28

iTrader: (9)

It doesnt matter hp/L. hp to weight is what counts.

My90Iroc

iTrader: (26)

The biggest differences between the lsx motors and the import motors you listed as a comparison are the valvetrains and the ability to run high rpms. If you build and LSX to run high rpms and flow sufficient air you'll hit the goal. As far as driveability and everything everyone has different degrees of tolerance as to what's ok and what's not. The problem with the street lsx motors and keeping a streetable rpm range. The more rpm you have the more gear you'll need for the real low speed stuff.

Louie83

iTrader: (3)

The shorter the stroke of the engine, the higher it's HP/L should be.

HP = TQ * RPM / 5252

Obviously, more RPM's = more HP. So in general, ricers (with strokes as long as my pinky) pull the HP/L argument know nothing about engines or physics.

ss53mech

I completely agree. But on a side note do you think the rod/stroke ratio is more of a deciding factor or the stroke bore ratio. I have seen the max efficient rpm capitalized on by utilizing a good rod stroke ration and valvetrain, but haven't really heard of people messing with different bore stroke combinations of the same displacement and the results created.

Formulated

iTrader: (16)

Variable valve timing will certainly make the achievement of streetability much easier. If any of you have experience with VTEC on Honda's, then you know what I'm talking about. I really think, though, that 4 valve cylinder heads are very important. I just don't think there's any other way to get volumetric efficiency up and keep then engine in a reasonable state of tune.

It's certainly possible to make 570hp with an LS1, or 600hp with and LS2, but many of the combinations that achieve that performance will be hard pressed to meet emissions standards, fuel economy requirements, reliability requirements, and driveability requirements. I think BMW's high output V8's are a good benchmark to see what is required for 100hp/l

Lythropus

iTrader: (13)

I second the 4 valve cylinder head being a major factor in hp/liter even though I consider it to be ricer math in the real world, it only counts if your limited displacement in a racing class...

Louie83

iTrader: (3)

4 valves per cylinder has a larger impact in higher RPM's. When the RPM's get up there, the valves open and shut much quicker. Having 4 valves can be useful in this situation to help move the air in the limited amount of time. This is why I would prefer a DOHC engine if I was working with a really short stroke.

With a long stroke, I would prefer the pushrod design since it is a smaller, more compact design.

TT632

iTrader: (3)

HP/liter, discussions are great to debate, but in the real world the drivabilty of high specific output vehicles is usually lacking due to poor low rpm performance.

Drivability and peak horse power don't usually go hand in hand . Average horsepower over the rpm your engine is operating in is what accelerates you. And, the average horse power in that operating range and the weight of the vehicle determines which car will be quickest. Peak horsepower on a Honda 4 cyl happens for an instant in time, not long enough to quickly accelerate you down the road.

You can have a 4 valve high specific output S2000 and you won't need a new LS7 vette to out accelerate it, an old L98 equipped car would do the trick.

jmdale1984

iTrader: (6)

Variable valve timing is an awesome idea, but this brings to mind the 2000-2003 Honda S2000 2.0L VTEC that made 240 hp. It peaked at 8500 I believe... and it made a fun little car to drive. Seemed to be a nice daily driver until I found out that it only did 26 mpg hwy according to the EPA. 98-02 V8 Fbodys were certified at 28 on the same rating. Seems like variable valve timing failed horribly in this instance.

chuntington101

TVR got very close to this magic goal of 100bhp per ltr with thier AJP V8s. the 4.5 made around 420bhp (often turned out to be less nce they left the factory). i have also read about a 5.7 ls1 making 600bhp na. it was a race motor with indavidual throtle bodies, but shows it CAN be done with the right stuff!

Chris.

Gannet

This is all exactly correct. The power/L is determined by the gas flow, and has nothing directly to do with any particular engine parameter such as stroke, number of valves, etc.

The difficulty is that if you want a large absolute number, like say 600, then you need a physically large engine (assuming NA). Metal doesn't move as fast or easy as gas because it is so dense. The forces generated by heavy parts moving at high speeds are hard to control, and hence require expensive engineering. So, large engines generally don't rotate at the speeds necessary for high specific output numbers. Small engines can make a high specific number due to the relatively smaller mass of their components, but they will have a lower absolute number.

As a generalization, for lowest initial cost and highest durability, build a large engine that turns slowly. If fuel economy, light weight, or emissions are a concern, then a smaller engine turning faster, and/or FI, may be required, but the $$/HP will go up and/or the engine life be shorter and/or maintenance will be higher.

And all that is exactly why Detroit built big-blocks for years. They were the best engineering solution, given the constraints at the time.

Shock Hawk

As far as drivability goes, I happen to like the current Impalas. They have a V8 (LS2 I think) and use a variable amount of cylinders. The engine wakes up and giddies up when you want it to, but it's just a plain sedan when you're just trying to go someplace. This is good.

I also like how some companies are making variable settings through the electronics on the car. A quick touch of a PDA screen can give you either mph or mpg.

Louie83

iTrader: (3)

I agree with everything but I'm not seeing how any of that shows how smaller strokes don't generally yield more peak HP/L.

Basically every single production car that does make 100hp/L does have a small stroke. If we took a 4 cylinder engine with 100HP/L, then doubled its stroke (if that were possible) then it would still more than likely make the same TQ/L, but it's HP/L would be significantly less. This can be seen just by looking at the Horsepower equation. Semi trucks make horrible HP/L, despite making good TQ/L. If you look the HP equation, and their stroke and RPM's, then it is clear why. S2000 = short stroke, high RPM, average TQ/L, high HP/L.

Ofcourse, if you go all out on a stroker motor (solid roller, dry sump) then you will be able to get crazy RPM's and a piston speed much greater than any Honda. Maybe it would be more "catch-all" if I stated high RPM's = more peak HP/L instead of just saying shorter strokes = more peak HP/L. But, I like to mention the stroke part because we have a whole generation that think Honda is superior to domestics because they don't understand engines or physics. Go to streetfire or some universal car site, and there are non-stop domestic vs import arguments, with the import crowd using HP/L as their crutch in every situation.

Formulated

iTrader: (16)

Come on guys, the Honda S2000 engine has a 90.7mm stroke, and the LS1 has a 92mm stroke. Very close, so stop talking about a short stroke being the solution.

The method Honda takes to achieving high specific output is high flow 4 valve cylinder heads, and VTEC. The high rpm lobes on a VTEC camshaft are really agressive. I had a set of aftermarket cams in my Prelude that had over 250 degrees duration a t .050", but the car idled like stock on the smaller set of lobes. The formula Honda uses for power is heavily weighted by engine speed. I just wish they made bigger engines. 120 hp/liter is great, but if you only have 2 liters, it's not much power.

This is why I think the BMW V8's are such a good benchmark for high specific output engines. BMW builds 100hp/liter V8s that meet all of the requirements put on passenger cars. The problem is that they are very complicated and expensive.

Any engine is a complex machine, and you can't just make passive statements that bore/stroke/etc... are the solution. There are lots of ways to get power. The important thing to realize is that we race cars, not dynos. And, we all have fixed budgets. That's where the LS1 is such a good platform. It's relatively simple, very robust, and not expensive. It's larger than the competition's engines, and appears to be not a very elegant solution. But, it is really very elegant when you take cost into consideration. By making the engine larger, GM can create lots of low speed power, and lower engine speed is better fuel economy.

I have lots of respect for the production high specific output engines by Honda and BMW because I love seeing technology. However, I like GM's solution better because it results in a better vehicle overall.

Gannet

Smaller strokes don't "yield", or cause, higher specific outputs (more hp/L). For a NA engine to make more hp/L, all else being equal, it has to be spun to higher RPMs. The two chief limiters on practical RPMs are valve train control and piston speed. Shorter strokes mean lower piston speeds for the same displacement. Put another way, all else being equal a shorter stroke engine can spin a higher RPM.

It would be the same as saying an OHC engine makes a higher specific output by virtue of it being OHC. Not true. OHCs make valve train control easier, and hence allow higher RPM, and hence such an engine can produce higher specific power. But the cam layout didn't "cause" that, and if you could get proper valve spring control at the same RPM without the OHC setup, you would make the same power.

In both cases, if you kept the RPM range of the short-stroke, OHC engine the same as the long-stroke OHV engine, they would make the same power (more or less). Or, if you had sufficient advances in metallurgy, etc. to allow the long-stroke OHV engine to spin as fast as the short-stroke OHC, it would make the same power.

Yes, this is all a bit of a simplification, as for example we are ignoring the effect of B/S ratio on breathing and combustion efficiency, but the majority of the reason for the designs you see are contained in the above, and previous.

All just IMO, and I make no claims to being an expert.

Gannet

Heh, nothing new about automotive enthusiasts that don't really understand why things work the way they do. "3/4-race" cam, anyone?

It's interesting that we (they) are measuring efficiency as output per liter of displacement. Why? Where does that come from?

Well, Europe has always been oil-poor. So, to prevent their balance of payments from getting out of whack, the Europeans started very early on to encourage excellent fuel economy. The "encouragement" took the form of high gasoline taxes, and also highly progressive yearly registration taxes on vehicles based on...you guessed it, engine displacement. Actually, they started out trying to tax horsepower directly, but the manufacturers played shenangians with their "advertised" ratings (surprise!) and the governments soon turned to something that could be easily measured.

The USA, being oil-rich, never went down that path. The size and power of our cars are not "artificially" constrained by onerous taxes, so our engineering solutions have been "more correct", in that they are solutions to meet the needs of the purchasers, not the Gov't. Well, until the late '60s, anyways.

From an engineering point of view, it would be much more interesting to talk about the power/$$ (both production and maintenance), or the power/weight, or the power/size, or the power/fuel used. Those are all relevant criteria when selecting an engine for an application. But power/displacement? An arbitrary measurement brought to you entirely by the tax man and racing commissioners, both of whom are looking for something that's easy to measure, not necessarily something that's real-world relevant, or that has anything to do with engineering.

Quick Double Nickel

iTrader: (5)

This is a great discussion. I wasn't trying to spark a debate on which type of engine is better or which method of measuring usable horsepower is better. I really just wanted some people to chime in on how it appears to be easier for some motors to obtain the 100 hp/l mark. The 100 hp/l mark is just arbitrary, it could have been 120 or 150 or 80. It seems like the common theme, though, is that it's easier for a smaller displacement motor to get there by virtue of the smaller mass of the rotating assembly and reduced amount of friction. Also, the increased need for more and more complex engine controls and valve control becomes necessary to reach the mark and maintain driveability.

There is no doubt the LSx motors are great motors, especially when you consider the initial cost and cost of maintenance/repairs. That's why I own one I just wanted to see if there is a way to improve on the already great foundation we have.

Cheatin' Chad

iTrader: (3)

This topic makes me wan to stab myself in my good eye......

Sharpe

iTrader: (7)

Where's the guy who has J-Rod's "HP/L is pretty much ricer math" quote in his sig when you need him?